Apparatus and System for Measuring Asphaltene Content of Crude Oil

ABSTRACT

A system for measuring asphaltene content of crude oil, includes a microfluidic chip, the microfluidic chip having a crude oil sample inlet port, a solvent port, a mixer and reactor section in fluid communication with the crude oil sample inlet port and the solvent port, and a filter in fluid communication with the mixer and reactor section, the filter having an inlet side and an outlet side, a waste port in fluid communication with the inlet side of the filter, and a product port in fluid communication with the outlet side of the filter. The system further includes an optical cell in fluid communication with the product port.

BACKGROUND

The measurement of asphaltene content of a hydrocarbon reservoir fluidis a common aspect of oil production, transportation, and refining.Because asphaltenes are not generally well defined and not wellunderstood, numerous methods have been developed for characterizing andquantifying asphaltenes in such reservoir fluids. Conventional methods,however, require large quantities of sample reservoir fluids andsolvents, large glass vessels, and many other instruments for properextraction of the asphaltenes. Typically, the quantification ofasphaltenes is performed by weighing asphaltenes extracted from thereservoir fluid, generally must be performed in a laboratoryenvironment, and require significant lengths of time to complete.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

In one aspect, the disclosed subject matter provides a system formeasuring asphaltene content of crude oil. The system includes amicrofluidic chip and an optical cell. The microfluidic chip comprises asample inlet port, a solvent port, and a mixer and reactor section influid communication with the sample inlet port and the solvent port. Themicrofluidic chip further includes a filter in fluid communication withthe mixer and reactor section, the filter having an inlet side and anoutlet side. The microfluidic chip further includes a waste port influid communication with the inlet side of the filter and a product portin fluid communication with the outlet side of the filter. The opticalcell is in fluid communication with the product port.

In another aspect, the disclosed subject matter provides a microfluidicchip. The microfluidic chip includes a sample inlet port, a solventport, and a mixer and reactor section in fluid communication with thesample inlet port and the solvent port. The microfluidic chip furtherincludes a filter in fluid communication with the mixer and reactorsection, the filter having an inlet side and an outlet side. Themicrofluidic chip further comprises a waste port in fluid communicationwith the inlet side of the filter and a product port in fluidcommunication with the outlet side of the filter.

In yet another aspect, the disclosed subject matter provides amicrofluidic chip. The microfluidic chip includes an upper portiondefining a sample inlet port, a solvent port, a waste port, a productport, a mixing channel, and a reactor channel, the mixing channel beingin fluid communication with the sample inlet port, the solvent port, andthe reactor channel. The microfluidic chip further includes anintermediate portion defining a further channel in fluid communicationwith the reactor channel. The microfluidic chip further includes amembrane filter in fluid communication with the further channel, themembrane filter having an inlet side and an outlet side. The waste portis in fluid communication with the inlet side of the membrane filter andthe product port is in fluid communication with the outlet side of themembrane filter. The desired filtration may also be achieved by othermeans such as a porous structure built into the microfluidic chip,settling chamber, or a centrifugal separator.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosed subject matter of the application aredescribed with reference to the following figures. The same numbers areused throughout the figures to reference like features and components.

FIG. 1 is a graphical representation illustrating a correlation model;

FIG. 2 is a schematic representation of a system for determining theoptical density of asphaltenes in a crude oil sample;

FIG. 3 is a schematic representation of a first illustrative embodimentof a microfluidic chip;

FIG. 4 is a top, plan view of a second illustrative embodiment of amicrofluidic chip;

FIG. 5 is a sectional, elevational view of the microfluidic chip of FIG.4;

FIG. 6 is a top, plan view of an upper portion of the microfluidic chipof FIG. 4;

FIG. 7 is a top, plan view of an intermediate portion of themicrofluidic chip of FIG. 4;

FIG. 8 is a top, plan view of a lower portion of the microfluidic chipof FIG. 4;

FIG. 9 is a schematic representation of a first illustrative embodimentof a system for measuring asphaltene content of crude oil; and

FIG. 10 is a schematic representation of a second illustrativeembodiment of a system for measuring asphaltene content of crude oil.

While the disclosed subject matter is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the disclosed subjectmatter of the application to the particular forms disclosed, but on thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the scope of the disclosed subject matter asdefined by the appended claims.

DETAILED DESCRIPTION

Illustrative embodiments of the disclosed subject matter of theapplication are described below. In the interest of clarity, not allfeatures of an actual implementation are described in thisspecification. It will of course be appreciated that in the developmentof any such actual embodiment, numerous implementation-specificdecisions must be made to achieve the developer's specific goals, suchas compliance with system-related and business-related constraints,which will vary from one implementation to another. Moreover, it will beappreciated that such a development effort might be complex andtime-consuming but would nevertheless be a routine undertaking for thoseof ordinary skill in the art having the benefit of this disclosure.

The disclosed subject matter of the application relates to an apparatusfor measuring the asphaltene content of a reservoir fluid, such as crudeoil.

Generally, asphaltenes are the heaviest and most polar components incrude oil. The asphaltene fraction of a crude oil sample is generallydefined as the fraction that is insoluble in an alkane, such as, forexample, n-heptane, but soluble in an aromatic hydrocarbon, such astoluene. The deasphalted fraction of crude oil is commonly referred toas the maltene fraction. Asphaltenes typically exhibit significantoptical absorbance or optical density in the visible light spectrum,while maltenes exhibit less optical absorbance or optical density in thevisible light spectrum than asphaltenes. Considering crude oil as acombination of asphaltenes and maltenes, with the asphaltene fractionand the maltenes fraction of a crude oil sample each exhibiting aparticular optical density or coloration, the linear addition of thedensity of each fraction results in the optical density or coloration ofthe crude oil sample. Comparison and calculation of the opticaldensities of crude oils and the crude oil fractions, that is, theasphaltenes and maltenes, is performed at substantially equalconcentrations. For example, if a fraction, such as an asphaltenefraction or a maltenes fraction, is extracted from a crude oil sample,the extracted volume is replaced by a transparent solvent.

The apparatus and system disclosed herein is used to indirectlydetermine the optical spectrum of the asphaltene fraction of a crude oilsample by subtracting the optical spectrum of the maltenes fraction fromthe optical spectrum of the crude oil sample. The asphaltene fraction isprecipitated from the crude oil sample and filtered, leaving themaltenes fraction. Precipitation and measurements are performed within amicrofluidic system on generally continuous fluid streams that aremaintained for a sufficiently long period of time to allowrepresentative and stable optical density measurements to be obtained.An example of such a determination is graphically shown in FIG. 1. Inthe optical density versus time graph shown on the left of FIG. 1, aline 101 graphically represents the optical density of a crude oilsample at a known wavelength. Line 103 graphically represents theoptical density of an asphaltene fraction of the crude oil sample andline 105 graphically represents the optical density of a maltenesfraction of the crude oil sample. The optical density of the asphaltenefraction of the crude oil sample at the known wavelength is determinedby subtracting the optical density of the maltene fraction of the crudeoil sample from the optical density of the crude oil sample includingboth asphaltenes and maltenes. The optical density versus asphaltenecontent graph shown on the right of FIG. 1 represents a correlationmodel generated using many different samples of crude oil. For example,data point 107 represents the optical density of the asphaltene fractionof a particular crude oil sample, while data point 109 represents theoptical density of the asphaltene fraction of another, differentparticular crude oil sample. Line 111 represents a linear fit of theoptical density versus asphaltene content data. Thus, the opticaldensity of the asphaltene fraction of a particular crude oil sample, forexample as represented by line 103, can be used to determine theasphaltene content of the particular crude oil sample within apredetermined tolerance range.

FIG. 2 is a graphical representation of a system 201 for determining theoptical density of asphaltenes in a crude oil sample. In the illustratedembodiment, a mixer 203, for example a microfluidic mixer, is in fluidcommunication with a microfluidic reactor 205. Microfluidic reactor 205is operably associated with a filter 207, for example, a membranefilter. Crude oil and an alkane, such as n-heptane, are introduced intomixer 203 wherein the crude oil and the alkane are mixed. The mixture iscommunicated into microfluidic reactor 205, wherein the asphaltenefraction is precipitated from the crude oil by the alkane, such that theasphaltene precipitate is dispersed in the maltene fraction. Themaltene/precipitated asphaltene mixture is communicated to filter 207,which filters out the asphaltene precipitate, allowing the maltenefraction to pass through. Mixer 203, microfluidic reactor 205, andfilter 207 are operatively associated to form a microfluidic chip 209.System 201 further comprises a spectrometer 211 in fluid communicationwith filter 207. The maltene fraction is communicated to spectrometer211, wherein the optical density of the maltene fraction is determined.

In one embodiment, system 201 of FIG. 2 is configured such that, asolvent, such as toluene, can be selectively introduced into mixer 203to aid in moving the crude oil through system 201 for the purpose ofdetermining the optical density of the crude oil. The crude oil and thesolvent are communicated though mixer 203, microfluidic reactor 205, andfilter 207 to spectrometer 211, wherein the optical density of the crudeoil is determined.

FIG. 3 depicts a schematic representation of an illustrative embodimentof a microfluidic chip 301, such as microfluidic chip 209, shown in FIG.2. In the illustrated embodiment, microfluidic chip 301 includes a crudeoil sample inlet port 303 and a solvent port 305. Solvent port 305 canbe used to introduce a solvent, such as toluene, or an alkane, such asn-heptane, to microfluidic chip 301 depending upon the particularoperation of microfluidic chip 301. Each of sample inlet port 303 andsolvent port 305 are in fluid communication with a mixer and reactorsection 307, which comprises one or more serpentine channels. In themixer portion of mixer and reactor section 307, the sample and the fluidintroduced via solvent port 305 are mixed. In the reactor portion ofmixer and reactor section 307, asphaltene in the sample precipitates asasphaltene flock disposed in maltenes when the crude oil sample is mixedwith an alkane. Microfluidic chip 301 further comprises a filter 309,such as a membrane filter, which is in fluid communication with mixerand reactor section 307. Filter 309 is configured to allow the maltenesto pass therethrough but not to allow the asphaltene flock to passtherethrough. The asphaltene flock can be flushed from microfluidic chip301 via a waste port 311 using a solvent introduced via solvent port305. The maltenes and residual alkane or solvent are collected frommicrofluidic chip 301 via a product port 313.

FIGS. 4-8 depict a microfluidic chip 401, which is a particularimplementation of microfluidic chip 301 of FIG. 3. FIG. 4 is a top, planview of microfluidic chip 401, while FIG. 5 is a sectional, elevationalview of microfluidic chip 401. As can be seen in FIG. 5, microfluidicchip 401 comprises an upper portion 501, an intermediate portion 503, afiltration membrane 505, and a lower portion 507. Filtration membrane505 is disposed between intermediate portion 503 and lower portion 507.Each of portions 501, 503, and 507 define certain channels fortransporting crude oil and/or other fluids through microfluidic chip401. Crude oil and solvent are introduced into upper portion 501 ofmicrofluidic chip 401, wherein the crude oil and solvent are mixed toinduce separation of asphaltenes from the crude oil. The asphaltenes arefiltered from the mixture by filtration membrane 505, allowing themaltenes and the remaining alkane or solvent to pass therethrough intolower portion 507. The maltenes and remaining alkane or solvent are thenrouted from microfluidic chip 401 via lower portion 507 and upperportion 501. To better illustrate the particular aspects of microfluidicchip 401, FIG. 6 depicts channels defined only in upper portion 501,FIG. 7 depicts channels defined only in intermediate portion 503, andFIG. 8 depicts channels defined only in lower portion 507.

Referring now to FIG. 6, upper portion 501 of microfluidic chip 401defines a sample inlet port 601, a solvent port 603, a product port 605,and a waste port 607. It should be noted that a solvent or an alkane maybe introduced into microfluidic chip 401 via solvent port 603 dependingupon the particular operation of microfluidic chip 401. Sample inletport 601 and solvent port 603 are channels defined by upper portion 501that lead from an edge 609 of upper portion 501 to a mixing channel 611defined by upper portion 501. In the illustrated embodiment, mixingchannel 611 is a microfluidic mixing channel, although other types ofmixing devices are contemplated. Mixing channel 611 is in fluidcommunication with a first serpentine channel 613, which routes fluidsthrough upper portion 501 of microfluidic chip 401 to a transfer port615, which is in fluid communication with a second serpentine channel701 (FIG. 7) defined by intermediate portion 503.

Referring now to FIG. 7, intermediate portion 503 of microfluidic chip401 defines a second serpentine channel 701, which routes fluids throughintermediate portion 503 of microfluidic chip 401. First serpentinechannel 613, shown in FIG. 6, defines a microfluidic reactor ofmicrofluidic chip 401, while the length of second serpentine channel 701determines the amount of asphaltenes that can be stored in microfluidicchip 401, and hence the amount of fluid that can be processed in onecycle. Within the microfluidic reactor, that is, within first serpentinechannel 613, alkane introduced via solvent port 603 reacts with thesample fluid to cause asphaltene precipitation. The microfluidic reactoris sufficient in length to allow adequate time for asphaltene flockgrowth within the microfluidic reactor. Second serpentine channel 701 isin fluid communication generally entirely with filtration membrane 505,shown in FIG. 5. Thus, fluids flowing through second serpentine channel701 are filtered by filtration membrane 505, such that fluids areallowed to pass through filtration membrane 505; however, particulates,such as asphaltene flock, are substantially retained by filtrationmembrane 505 and not allowed to pass therethrough. Second serpentinechannel 701 is also connected to waste port 607 by transfer port 616.

Referring now to FIGS. 6 and 8, filtered fluid is collected in a filterchannel 801, and then routed via a product channel 803, each defined bylower portion 507. In the illustrated embodiment, filter channel 801exhibits substantially the same shape as second serpentine channel 701of intermediate portion 503, shown in FIG. 7. Product channel 803 is influid communication with product port 605 via a transfer port 617.Transfer port 617 and product port 605 are each defined by upper portion501. The filtered fluid is subsequently inspected, such as by usingoptical spectroscopy, to determine the optical density of the filteredfluid. Referring in particular to FIG. 6, waste, that is, the materialsthat do not pass through filtration membrane 505, are routed or flushedto waste port 607.

Referring in particular to FIG. 5, in one embodiment, upper portion 501and intermediate portion 503 may comprise B 270® glass, available fromSCHOTT North America, Inc. of Elmsford, N.Y., USA, fused silica, or thelike. In one embodiment, upper portion 501 is generally about onemillimeter thick and intermediate portion 503 is generally about twomillimeters thick. Channels, ports, and the like defined by upperportion 501 and/or intermediate portion 503 are, in one embodiment,etched isotropically into the portions using, for example, a wet etchingprocess. In one embodiment, one, some, or all of the channels, ports,and the like defined by upper portion 501 and intermediate portion 503exhibit a plurality of depths, ranging from about 50 micrometers toabout 250 micrometers and are produced using a multi-phase maskingprocess. In one embodiment, lower portion 507 comprisespolyetheretherketone (PEEK). In one embodiment, components ofmicrofluidic chip 401 are mounted in a chip holder to locate thecomponents relative to one another. In one embodiment, the chip holderincludes a case housing highly-sprung bolts arranged about microfluidicchip 401. In a certain embodiment, when the bolts reach a “dead-stop”,the clamp provides a compression force of about 600 Newtons to create apartial seal over filtration membrane 505. Thus, fluid passing throughfiltration membrane 505 is collected downstream of membrane 505 in thechip holder and guided to the output for analysis, while precipitatedasphaltene flocks are held back and collect on the filtration membrane505. In one embodiment, filtration membrane 505 comprises apolytetrafluoroethylene (PTFE) membrane with an average pore size ofabout 200 nm; however, membranes made of other materials and withdifferent pore sizes are also contemplated.

FIG. 9 depicts a first illustrative embodiment of a system 901 formeasuring asphaltene content of crude oil. System 901 is depicted ascomprising microfluidic chip 301, shown in FIG. 3; however, system 901may comprise microfluidic chip 401, shown in FIGS. 4-8, or any otherconfiguration contemplated by the disclosure or its equivalent. In theillustrated embodiment, system 901 comprises a sample loop 902 in whicha sample of crude oil is disposed after having been injected therein by,for example, a syringe pump, from crude oil sample reservoir 903 througha first switching valve 904. Sample loop 902 is in fluid communicationwith a first solvent pump 905 and sample inlet port 303 of microfluidicchip 301. System 901 further comprises an alkane pump 907 and a secondsolvent pump 909, each of which are selectively in fluid communicationwith solvent port 305 of microfluidic chip 301 via a second switchingvalve 911. In one embodiment, first solvent pump 905, second solventpump 909, and alkane pump 907 are syringe pumps. System 901 furthercomprises an optical cell 913, such as a spectrometer, in fluidcommunication with product port 313 of microfluidic chip 301.

In a first particular operation of system 901, crude oil from samplereservoir 903 is first injected into sample loop 902 through firstswitching valve 904. Thereafter, the alignment of first switching valve904 is switched and a solvent, such as toluene, is urged into sampleloop 902 by first solvent pump 905 to urge the crude oil sample disposedtherein into sample inlet port 303 of microfluidic chip 301. Secondswitching valve 911 is configured to allow second solvent pump 909 tourge a solvent, such as toluene, into solvent port 305 of microfluidicchip 301. As asphaltenes are soluble in such solvents, no asphalteneprecipitation occurs; the crude oil sample is merely diluted. Thediluted oil sample passes through filter 309 substantially in itsentirety. In one embodiment, system 901 operates first solvent pump 905and second solvent pump 909 to introduce the solvent into microfluidicchip 301 at a mixing ratio to dilute the crude oil sample sufficientlyso that optical cell 913 can determine the optical density of thediluted crude oil. In this way, the same system 901 can be used to bothdetermine the optical density of crude oil and the maltene component ofcrude oil.

In a second particular operation of system 901, a solvent, such astoluene, is urged into sample loop 902 by first solvent pump 905 to urgethe crude oil sample disposed therein into sample inlet port 303 ofmicrofluidic chip 301. Second switching valve 911 is then configured toallow alkane pump 907 to urge an alkane, such as n-heptane, into solventport 305 of microfluidic chip 301. In one embodiment, system 901operates first solvent pump 905 and alkane pump 907 to introduce thealkane into microfluidic chip 301 at a predetermined mixing ratio, suchas 40 parts alkane to one part crude oil. The alkane and crude oil aremixed and the resulting flocculated asphaltenes are filtered, leavingmaltenes and residual alkane material, as described herein regardingmicrofluidic chips 301 and 401. The maltenes and residual alkanematerial are then routed to optical cell 913 to determine their opticaldensity.

FIG. 10 depicts a second illustrative embodiment of a system 1001 formeasuring asphaltene content of crude oil. System 1001 is depicted ascomprising microfluidic chip 301, shown in FIG. 3; however, system 1001may comprise microfluidic chip 401, shown in FIGS. 4-8, or any otherconfiguration contemplated by the disclosure or its equivalent. In theillustrated embodiment, system 1001 comprises a first solvent pump 1003,an alkane pump 1005, and a second solvent pump 1007. Alkane pump 1005 isoperable to urge an alkane, such as n-heptane, therefrom, while secondsolvent pump 1007 is operable to urge a solvent, such as toluene,therefrom. In one embodiment, alkane pump 1005 is in fluid communicationwith a stock alkane reservoir 1009 via a valve 1011 and solvent pump1007 is in fluid communication with a stock solvent reservoir 1013 via avalve 1015. In one embodiment, one or more of first solvent pump 1003,alkane pump 1005, and second solvent pump 1007 are syringe pumps, suchas Mitos Duo XS pumps, available from The Dolomite Center Limited ofRoyston, Hertfordshire, UK. In one embodiment, valves 1011 and 1015 arepart of the respective syringe pumps and are rated for pressures up toabout six bars. In one embodiment, alkane pump 1005 and second solventpump 1007 are configured to automatically fill when filling is needed.System 1001 further comprises a computer-controllable, six-port, two-wayswitching valve 1017, such as Cheminert Valve C22-3186, available fromVICI Valco Instruments Co., Inc. of Houston, Tex., USA. In oneembodiment, valve 1017 is rated for liquid pressures of about 16 bar.

Still referring to FIG. 10, when configured in a first position, valve1017 places a filter 1019 in fluid communication with a crude oil sampleloop 1021 and a waste port 1023. In one embodiment, filter 1019comprises a dead-volume filter, such as a solvent filter assembly A-335,available from Upchurch Scientific, IDEX Health & Science LLC of OakHarbor, Wash., USA. In such an embodiment, the filter includes a frit ofabout 10 micrometers, such as Semi-prep PEEK frit A-720, provided byUpchurch Scientific. An oil sample can be loaded manually, such as via asyringe, into sample loop 1021 via filter 1019 to remove largeparticulates before entering system 1001. In one embodiment whereinasphaltene content is to be measured, sample loop 1021 exhibits a volumeof about 180 microliters. Additional crude oil may be required due todead volume in filter 1019 and upstream of filter 1019 and foroverfilling sample loop 1021. In one particular operation, about 250microliters of crude oil is used to load sample loop 1021. First solventpump 1003 is operable to urge a solvent, such as toluene, into sampleloop 1021 via valve 1017 in a second position to urge a crude oil samplefrom sample loop 1021. Sample loop 1021 is in fluid communication withsample inlet port 303 of microfluidic chip 301 via valve 1017.

The outputs of alkane pump 1005 and second solvent pump 1007 are mergedin a Y section 1025 and are both in fluid communication with a pressuresensor 1027, such as model 40PCXXXG2A, available from Honeywell Sensingand Control of Golden Valley, Minn., USA, such that the indicator “XXX”corresponds to the desired pressure range in pounds per square inch.Although pressure sensor 1027 is shown in FIG. 10 as being an in-linesensor, the scope of the disclosure encompasses embodiments whereinpressure sensor 1027 is a dead-end pressure sensor in fluidcommunication with a T-junction in the flow line. Pressure sensor 1027functions to detect an overpressure of system 1001, such as may resultfrom excessive asphaltene build up, so that the operation of system 1001can be halted. Pressure sensor 1027 can also function so that fluiddispensing can be adjusted to maintain pressure levels within thepressure rating of system 1001. Alkane pump 1005 and second solvent pump1007 are in fluid communication with solvent port 305 of microfluidicchip 301.

Referring still to FIG. 10, product port 313 of microfluidic chip 301 isin fluid communication with an optical cell 1029, operable to determinean optical density of fluid emitted from product port 313. In oneembodiment, optical cell 1029 comprises an optical absorbance flow cell,such as a 2.5 mm optical path FIAlab SMA-Z-uvol cell with fused silicawindows (SMA-Z-2.5-uvol), available from FIAlab Instruments, Inc. ofBellevue, Wash., USA. The optical flow cell is connected via fiberoptics to a broadband light source based on a tungsten filament bulb,such as a model LS-1 light source available from OceanOptics, Inc. ofDunedin, Fla., USA, and to a broadband spectrometer, such as a modelHR2000+ provided by OceanOptics, Inc. In one embodiment, thespectrometer is computer controlled. Waste port 311 of microfluidic chip301 is in fluid communication with a switching valve 1031 to selectivelyallow fluid flow from waste port 311. In one embodiment, switching valve1031 is a 2/2, on/off, direct lift solenoid valve, such as a modelS-01540-03, available from Cole-Parmer Canada, Inc. of Montreal, Quebec,Canada. Switching valve 1031 inhibits flow therethrough during normaloperation and allows flow during cleaning of filter 309 of microfluidicchip 301.

In certain embodiments, system 1001 utilizes tubing with 1/16-inch (1.6mm) outer diameter and ¼-28 flat bottom flangeless fittings. The tubingmaterials used, in some embodiments, are fluorinated ethylene propylenewhere high transparency is required and ethylene tetrafluoroethylene(Tefzel® available from E.I. du Pont de Nemours and Company ofWilmington, Del., USA) elsewhere due to its more rigid structure. Incertain embodiments, the inner diameter of such tubing is 0.01 inch(0.25 mm) for minimal dead volume on all feed and product lines and 0.03inch (0.76 mm) for waste lines, in order to reduce flow resistance.

In one particular operation of system 1001, system 1001 is purged. Firstsolvent pump 1003, alkane pump 1005, and second solvent pump 1007 areoperated at high flow rates and valves 1011, 1015, 1017, and 1031 areoperated to remove air bubbles and air pockets from components of system1001.

System 1001 is then primed with solvent. With valve 1031 open, solventpump 1007 is operated to dispense solvent at a high flow rate intomicrofluidic chip 301 and system 1001 until residual alkane isdisplaced. Valve 1031 is then closed.

The integrity of filter 309 of microfluidic chip 301 is then tested withsolvent. Second solvent pump 1007 is operated to dispense solventthrough microfluidic chip 301 and optical cell 1029 at about 1200microliters per minute, at about 600 microliters per minute, and atabout 300 microliters per minute. The flow at each rate is sustained fora sufficient amount of time to obtain a stable pressure plateau forabout 20 seconds each. Delays are performed between pressure pulses toallow the pressure to dissipate to the background level.

Reference values are then determined for optical cell 1029. The spectrallight transmission through the cleaned flow cell of optical cell 1029,primed with solvent, is captured and stored as a white reference. Thelight source is blocked while a second spectral response is captured andstored as a dark reference.

The crude oil sample is then pre-injected into system 1001. All syringesare filled for a synchronous start. Valve 1017 is activated. Firstsolvent pump 1003 and alkane pump 1005 are activated to introduce thecrude oil sample and alkane, respectively, into microfluidic chip 301.Higher flow rates can be used until the heart of the crude oil slugreaches the mixer inlet of microfluidic chip 301 to save cycle time. Incertain operations, solvent is added to the mixer of microfluidic chip301 at a moderate rate to decrease fluid viscosity.

System 1001 is then flushed with solvent. Second solvent pump 1007 isoperated to flush solvent through system 1001 to remove oil frommicrofluidic chip 301 and optical cell 1029. Crude oil sample, however,remains in the sample feed line to sample inlet port 303 of microfluidicchip 301.

A diluted crude oil run is then performed. All syringes are filled for asynchronous start. First solvent pump 1003 and second solvent pump 1007are activated to urge the crude oil sample and solvent, respectively,into microfluidic chip 301. In certain operations, first solvent pump1003 is operated to introduce crude oil into microfluidic chip 301 at arate of about ten microliters per minute, while second solvent pump 1007is operated to introduce solvent into microfluidic chip 301 at a ratewithin a range of about 400 microliters per minute to 1000 microlitersper minute, depending on the type of crude oil sample. In one particularoperation, flow is maintained for about five minutes. As the mixture isurged through microfluidic chip 301 and optical cell 1029, absorbancesignals at a wavelength of about 600 nanometers are recorded over time.The duration of the run is sufficient so that a stable absorbance valueis recorded for about three minutes.

System 1001 is then flushed with solvent. Second solvent pump 1007 isoperated to flush solvent through system 1001 to remove oil frommicrofluidic chip 301 and optical cell 1029. Crude oil sample, however,remains in the sample feed line to sample inlet port 303 of microfluidicchip 301.

Microfluidic chip 301 is then primed with alkane. Alkane pump 1005dispenses alkane at a high flow rate into microfluidic chip 301 andoptical cell 1029 until residual toluene is displaced.

The integrity of filter 309 of microfluidic chip is then tested withalkane. Alkane pump 1005 is operated to dispense alkane throughmicrofluidic chip 301 and optical cell 1029 at about 1200 microlitersper minute, at about 600 microliters per minute, and at about 300microliters per minute. The flow at each rate is sustained for asufficient amount of time to obtain a stable pressure plateau for about20 seconds each. Delays are performed between pressure pulses to allowthe pressure to dissipate to the background level.

Reference values are then determined for optical cell 1029. The spectrallight transmission through the cleaned flow cell of optical cell 1029,primed with alkane, is captured and stored as a white reference. Thelight source is blocked while a second spectral response is captured andstored as a dark reference.

A maltene separation run is then performed. All syringes are filled fora synchronous start. First solvent pump 1003 and alkane pump 1005 areactivated to urge the crude oil sample and alkane, respectively, intomicrofluidic chip 301. In certain operations, first solvent pump 1003 isoperated to introduce crude oil into microfluidic chip 301 at a rate ofabout ten microliters per minute, while alkane pump 1005 is operated tointroduce alkane into microfluidic chip 301 at a rate of about 400microliters per minute. In one particular operation, flow is maintainedfor about five minutes. As the mixture is urged through microfluidicchip 301 and optical cell 1029, absorbance signals at a wavelength ofabout 600 nanometers are recorded over time. The duration of the run issufficient so that a stable absorbance value is recorded for about threeminutes.

System 1001 is then cleaned. Valve 1031 is switched to the open positionand second solvent pump 1007 is operated to urge solvent intomicrofluidic chip 301 at a rate of about 500 microliters per minute,urging solvent toward filter 309 of microfluidic chip 301 to dissolveasphaltene deposits. If solvent injection pressure exceeds about threebar, operation of second solvent pump 1007 is paused and only resumed ifthe pressure drops below about 2.5 bar. After substantially allasphaltene is dissolved and pressure is maintained at a normal level,solvent flow is maintained while first solvent pump 1003 operates at aflow rate of about 50 microliters per minute until crude oil in thesample feed line is displaced. First solvent pump 1003 and secondsolvent pump 1007 then operate at maximum flow rate as all valves areswitched to ensure complete cleaning of system 1001 and to substantiallyfill system 1001 with clean solvent.

The integrity of filter 309 of microfluidic chip 301 is then tested withsolvent. Second solvent pump 1007 is operated to dispense solventthrough microfluidic chip 301 and optical cell 1029 at about 1200microliters per minute, at about 600 microliters per minute, and atabout 300 microliters per minute. The flow at each rate is sustained fora sufficient amount of time to obtain a stable pressure plateau forabout 20 seconds each. Delays are performed between pressure pulses toallow the pressure to dissipate to the background level.

Although only a few example embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications are possible in the example embodiments without materiallydeparting from this invention. Accordingly, all such modifications areintended to be included within the scope of this disclosure as definedin the following claims. In the claims, means-plus-function clauses areintended to cover the structures described herein as performing therecited function and not only structural equivalents, but alsoequivalent structures.

What is claimed is:
 1. A microfluidic chip, comprising: a sample inletport; a solvent port; a mixer and reactor section in fluid communicationwith the sample inlet port and the solvent port; a filter in fluidcommunication with the mixer and reactor section, the filter having aninlet side and an outlet side; a waste port in fluid communication withthe inlet side of the filter, and; a product port in fluid communicationwith the outlet side of the filter.
 2. The microfluidic chip of claim 1,wherein the mixer and reactor section comprises a microfluidic mixer. 3.The microfluidic chip of claim 2, wherein the microfluidic mixerexhibits a serpentine shape.
 4. The microfluidic chip of claim 1,wherein the mixer and reactor section comprises at least onemicrofluidic reactor.
 5. The microfluidic chip of claim 4, wherein theat least one microfluidic reactor exhibits a serpentine shape.
 6. Themicrofluidic chip of claim 1, wherein the filter is a membrane filter.7. A microfluidic chip, comprising: an upper portion defining a sampleinlet port, a solvent port, a waste port, a product port, a mixingchannel, and a reactor channel, the mixing channel being in fluidcommunication with the sample inlet port, the solvent port, and thereactor channel; an intermediate portion defining a further channel influid communication with the reactor channel; and a membrane filter influid communication with the further channel, the membrane filter havingan inlet side and an outlet side; wherein the waste port is in fluidcommunication with the inlet side of the membrane filter and the productport is in fluid communication with the outlet side of the membranefilter.
 8. The microfluidic chip of claim 7, further comprising a lowerportion defining a product channel, the product channel being in fluidcommunication with the outlet side of the membrane filter and theproduct port.
 9. The microfluidic chip of claim 8, wherein the lowerportion comprises polyetheretherketone.
 10. The microfluidic chip ofclaim 8, wherein the lower portion further defines a filter channelcorresponding to the further channel, the filter channel being in fluidcommunication with the outlet side of the membrane filter and theproduct channel.
 11. The microfluidic chip of claim 7, wherein at leastone of the reactor channel and the further channel are serpentine inconfiguration.
 12. The microfluidic chip of claim 7, wherein at leastone of the reactor channel and the further channel are microfluidicchannels.
 13. The microfluidic chip of claim 7, wherein the upperportion and the intermediate portion comprise one of glass or fusedsilica.
 14. A system for measuring asphaltene content of crude oil,comprising: a microfluidic chip, the microfluidic chip comprising: acrude oil sample inlet port; a solvent port; a mixer and reactor sectionin fluid communication with the crude oil sample inlet port and thesolvent port; a filter in fluid communication with the mixer and reactorsection, the filter having an inlet side and an outlet side; a wasteport in fluid communication with the inlet side of the filter, and; aproduct port in fluid communication with the outlet side of the filter;and an optical cell in fluid communication with the product port. 15.The system of claim 14, further comprising: a first solvent pump; and asample loop in fluid communication with the first solvent pump and thecrude oil sample inlet port.
 16. The system of claim 14, furthercomprising: an alkane pump in fluid communication with the solvent port;and a second solvent pump in fluid communication with the solvent port.17. The system of claim 16, further comprising: an alkane reservoir influid communication with the alkane pump; and a solvent reservoir influid communication with the second solvent pump.
 18. The system ofclaim 17, wherein at least one of the alkane pump and the second solventpump are configured to refill themselves from the alkane reservoir andthe solvent reservoir, respectively.
 19. The system of claim 16, whereinthe alkane pump and the second solvent pump are each in selective fluidcommunication with the solvent port.
 20. The system of claim 14, whereinthe optical cell comprises a spectrometer.
 21. The system of claim 20,wherein the optical cell further comprises an optical flow cell.